Production of precoated metal materials has recently been increasing to a great extent. Such materials are those which have been painted or coated prior to being subjected to shaping processes, and provide a very convenient process for the production of shaped metallic articles when compared with a process in which the material is shaped into an article, e.g. by pressing, and thereafter painted.
Usually, precoated metal materials have heretofore been prepared by applying a thermocurable paint onto a surface-treated metal substrate to form a layer of the paint on the substrate and, then, thermally curing the paint. Other processes wherein a thin film is hot-pressed or adhesively bonded onto a metal sheet to provide an integral laminate, have also been practiced.
Precoated metal materials not only have out-door applications as materials for roofs and side walls, but also have in-door applications as materials for inside walls, cabinets and domestic electrical instruments. Thus, such precoated metal materials are required to have, in addition to corrosion resistance, weatherability and processability for our-door use, as well as processability and resistance to chemicals for in-door use. In addition to these, other properties, including resistance to water, resistance to boiling water, soil resistance, elongation and aesthetic requirements, are also necessary and the required level of each property is considerably high.
United Kingdom patent specification No. 1,302,515 discloses a radiation curable coating composition suitable for use in coating metal substrates, comprising an acrylic copolymer, at least one cross-linking agent whose molecule comprises two or three ethylenic unsaturations and at least one ethylenically unsaturated monomer. When the composition proposed in the U.K. patent is applied to a metal substrate and then suitably irradiated with an electron beam, a hard coating firmly adherent to the substrate, may be formed on the substrate.
In accordance with the present invention it has now been found that if a suitable shock absorber is added to the coating composition disclosed in the U.K. patent, the resultant coating composition can provide, on a metal substrate, a coating which has an improved impact strength and in turn an enhanced processability which is highly desirable for precoated metal materials, without adversely affecting other desirable properties of the coating, such as excellent hardness and high resistance to water and chemicals.